Patent GB-860247-A (GB)
Title: Improvements in or relating to photographic camera exposure time regulation
IPC: G03B9/64
Filed: 1958-11-27
Abstract: 860,247. Photo-electric control of photographic exposure. GAUTHIER G.m.b.H., A. Nov. 27, 1958 [Feb. 12, 1958], No. 38237/58. Class 40 (3). [Also in Group XX] The duration of a photographic exposure is determined by the time taken for the needle of a photo-electric exposure meter (or the equivalent) to travel from the position to which it has been set in response to the prevailing light conditions to an extreme position to which it is moved by connection to a battery when the exposure is initiated. To allow for the use of different stops, the camera diaphragm is geared to a diaphragm or grey wedge through which the light reaches the photo-cell and to allow for the use of different film speeds, the point at which the gears engage is adjustable. Two arrangements are described. In each case, operation of a lever to initiate an exposure causes the connection of the meter movement to a battery and the opening of the shutter which is then latched open. When the meter reaches its extreme position it completes a circuit for an unlatching magnet which allows the shutter to close. Alternatively, the meter movement may act mechanically on the shutter but this arrangement is not described in detail. In both cases there is a time delay between the connection of the meter to the battery and the opening of the shutter to compensate for the time taken for the unlatching operation. Detailed working. In the arrangement shown in Figs. 1 and 3, setting lever 4 is operated in the usual way to tension the driving spring 5 and also the spring 58 of a delay train. Operation of the exposure lever 12 releases the driving member 4 and the shutter blade ring 3 moves by an amount sufficient to allow contacts 43, 44 to close and connect battery 24 to the movement of a meter previously under control of a photo-cell at 15. At the same time an arm 3a on the ring trips a delay train by engagement with a lever 69 and then engages a lever 71 which prevents further movement of the ring. When the train has run down, lever 71 is moved clear and the ring 3 continues to rotate until the shutter is open and is then latched by the armature of an electromagnet 35. When the meter movement reaches its extreme position, 35 is energized to release ring 3 and the shutter completes its operation, and re-opens contacts 43, 44. In the arrangement shown in Fig. 5, the delay between the closing of contacts 49, 50 to connect the battery to the meter and the opening of the shutter is given by having the driving member in two parts with a lost motion connection between them. When the exposure lever 12 is actuated, the spring 5 drives the part 4 allowing the contacts to close and, when the upper part of slot 4c engages pin 74, drives shutter blade ring 3 in the usual way. The shutter is latched in its open position by engagement of a hook on lever 75 with a step on member 4. When the meter reaches its extreme position it energizes magnet 35 which, by means of a cable connection 79, swings lever 75 clear and allows the shutter to close. Calibration. Switch 83 is provided to enable the meter to be connected manually to the battery via an adjustable resistor which is set to bring the needle to a predetermined point on the scale. During this operation, the photocell is disconnected at 84. A further adjustable resistor 34 is included in the photo-cell circuit.